Ceramic preform and method

ABSTRACT

The present application discloses a ceramic preform, a method of making a ceramic preform and a metal matrix composite comprising a ceramic preform. In one exemplary embodiment, the ceramic preform comprises a ceramic compound compressed into the shape of a cylinder by rotational compression molding. The cylinder has an inner surface and an outer surface. A first liner may be attached to the inner surface of the cylinder and a second liner may attached to the outer surface of the cylinder. The metal matrix composite of the present application may be formed as a brake drum or a brake disc.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 13/886,113, filed May 2, 2013, now U.S. Pat. No.9,429,202, issued Aug. 30, 2016, and titled “CERAMIC PREFORM AND METHOD,which claims priority to U.S. Provisional Patent Application No.61/641,561, filed on May 2, 2012 and titled “Method for Making a CeramicPreform,” which is hereby incorporated by reference in its entirety.

BACKGROUND

A metal matrix composite (MMC) is generally made by incorporating areinforcing material into a metal matrix. For example, a MMC maycomprise a ceramic preform that is infiltrated with a metal. A MMCgenerally has properties and physical characteristics different frommetal that may be desirable depending on the application. One method ofmaking a ceramic preform for a MMC involves extruding a ceramiccomposition to form the ceramic preform. However, this method of makinga ceramic preform does not lend itself to high volume manufacturing.

Vehicles may include drum brakes and/or disc brakes. A drum brakegenerally comprises a rotating drum-shaped part called a brake drum.Shoes or pads of the drum brake press against the interior surface ofthe brake drum to cause friction and reduce the rotation of the brakedrum. A disc brake generally comprises a rotating brake disc or rotor.Calipers having brake pads that squeeze the exterior and interior of thebrake disc to cause friction and reduce the rotation of the brake disc.During the vehicle braking process there is often a high energy transferto the frictional surface of the brake drum or brake disc which can leadto a rise in temperature, sometimes as high as 700 degrees C. for heavyvehicles such as large trucks or military vehicles.

SUMMARY

The present application discloses a ceramic preform, a method of makinga ceramic preform, an apparatus for making a ceramic preform, a MMCcomprising a ceramic preform, and a method of making a MMC.

In certain embodiments, the ceramic preform comprises a ceramic compoundcompressed into the shape of a cylinder by rotational compressionmolding. The cylinder has an inner surface and an outer surface. A firstliner is attached to the inner surface of the cylinder and a secondliner is attached to the outer surface of the cylinder. In certainembodiments, the metal matrix composite comprises a ceramic preformformed in the shape of a cylinder by rotational compression molding andinfiltrated with a molten metal. The metal matrix composite may beformed as a brake drum and the ceramic preform may form at least aportion of a braking surface of the brake drum. The metal matrixcomposite may also be formed as a brake disc and the ceramic preform mayform at least a portion of a braking surface of the brake disc.

In certain embodiments, the method of making a ceramic preform comprisesutilizing a compression molding apparatus having a first die portion anda second die portion. One or more porous and/or absorbent liners areplaced on at least one surface of the first die portion and the seconddie portion. The one or more liners generally adhere to the ceramicpreform instead of to the mold surface, facilitating removal of thepreform from the mold. The absorbency of the liner, which may be acardboard core in certain embodiments, helps to draw the moisture fromthe preform before burning the organics out of the preform. A ceramiccompound is placed in the second die portion. The ceramic compound iscompressed with the first die portion to form a ceramic preform. Whenthe ceramic preform is removed from the compression molding apparatus,the one or more liners are attached to one or more surfaces of theceramic preform. In certain embodiments, the one or more porous and/orabsorbent liners comprise a first liner and a second liner, the firstdie portion is a male die portion, and the second die portion is afemale die portion. Further, the first liner is shaped as a cylindricaltube and disposed about one end of the male die portion and the secondliner is shaped as a cylindrical tube and received within the female dieportion. When the ceramic preform is removed from the compressionmolding apparatus, the first liner is attached to an inner diametersurface of the ceramic preform and the second liner is attached to anouter diameter surface of the ceramic preform.

In certain embodiments, the method of making a ceramic preform comprisesutilizing a compression molding apparatus having a first die portion anda second die portion. A ceramic compound is placed in the second dieportion and compressed with the first die portion to form a ceramicpreform. The first die portion is rotating about its longitudinal axisand relative to the second die portion during compression of the ceramiccompound. The ceramic preform is removed from the compression moldingapparatus.

These and additional embodiments will become apparent in the course ofthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are incorporated in and constitute apart of the specification, embodiments of the invention are illustrated,which, together with a general description of the invention given above,and the detailed description given below, serve to example theprinciples of the inventions.

FIG. 1 illustrates a method of making a ceramic preform according to anembodiment of the present application.

FIG. 2 illustrates a method of making a ceramic compound according to anembodiment of the present application.

FIG. 3A illustrates a method of forming a ceramic preform according toan embodiment of the present application.

FIG. 3B illustrates a method of forming a ceramic preform according toan embodiment of the present application.

FIGS. 4A-4C illustrate a compression molding apparatus according to anembodiment of the present application, wherein the apparatus is shownforming a ceramic preform of the present application.

FIGS. 5A and 5B are perspective and cross sectional views, respectively,of a ceramic preform according to an embodiment of the presentapplication.

FIG. 6 is a cross sectional view of a ceramic preform according to anembodiment of the present application.

FIG. 7 is a cross sectional view of a metal matrix composite brake drumaccording to an embodiment of the present application.

FIG. 8A is a side view of a metal matrix composite brake disc accordingto an embodiment of the present application.

FIG. 8B is a cross sectional view of the metal matrix composite brakedisc of FIG. 8A taken along line 8B-8B.

FIGS. 9A and 9B are top and cross sectional views, respectively, of aceramic preform according to an embodiment of the present application.

DESCRIPTION OF EMBODIMENTS

The present application discloses a ceramic preform, a method of makinga ceramic preform, an apparatus for making a ceramic preform, a MMCcomprising a ceramic preform, and a method of making a MMC. The MMC ofthe present application is generally less dense, lighter, stronger athigher temperatures and provides higher wear resistance than certainmetal, non-composite materials. For example, an aluminum MMC of thepresent application generally has greater wear resistance and stiffness(i.e., resistance to deformation) than cast iron. As such, the MMC ofthe present application is useful in applications where high wearresistance and strength is beneficial.

The MMC of the present application may be formed as a brake drum, brakedisc or rotor, or any component thereof for a vehicle. For example, theceramic preform of the present application may be infiltrated with ametal, such as, for example, aluminum, magnesium, titanium, or copper,and form at least a portion of a brake drum or brake disc or rotor. Inparticular, the MMC of the present application generally forms at leasta portion of the braking surface of the brake drum or brake disc. Thebraking surface for the brake drum is generally located on the interiorsurface of the brake drum that contacts the shoes or pads of the drumbrake. The braking surface for the disc brake is generally located onthe surfaces of the brake disc that contact the brake pads. The brakedrum or brake disc of the present application may be used for virtuallyany vehicle, including but not limited to, aircraft, trucks, vans, cars,military vehicles, construction vehicles, motorcycles, SUVs, ATVs, andXUVs. However, the MMC of the present application may be formed as avariety of other items, such as, for example, bearings, pistons,cylinder liners, piston rings, connecting rods, aerospace components,armor, or the like.

The MMC brake drums and brake discs of the present application generallyhave greater wear resistance and less weight than a conventional castiron brake drums or brake discs. One exemplary method of making a MMCbrake drum or brake disc is to insert a ceramic preform of the presentapplication into a high pressure die casting machine. Molten metal(e.g., aluminum) is then injected under high pressure into the die. Themolten metal will infiltrate the porous and/or absorbent ceramic preformand fill the die to produce the MMC brake drum. One difficulty found inconventional MMC brake drum manufacturing processes is developing apreform with enough strength (e.g., hoop strength) such that it doesn'tbreak during the handling process, the machining process or when thehigh pressure molten metal is injected filling the preform and the die.The methods and apparatuses for forming a ceramic preform described inthe present application produce a part that is stronger and moredimensionally stable than ceramic preforms made by conventionalprocesses.

FIG. 1 illustrates an exemplary method 100 of making a ceramic preformaccording to an embodiment of the present application. As shown, themethod 100 comprises the steps of fiber preparation, preparation of aceramic compound, compression molding of the ceramic compound to form aceramic preform, drying, heat treatment for binder burnout, and heattreatment for inorganic binder setting. These steps are described ingreater detail below.

The ceramic compound used to make the ceramic preform of the presentapplication may comprise ceramic particles, reinforcing fiber, fugitiveporosity-generating component, starch, organic low temperature binder,colloidal silica suspension, and water. The table below shows typicalweight percentage ranges for each component of the ceramic compoundaccording to an embodiment of the present application.

Component Weight Percentage, Wt % Ceramic Particles 20 to 55 ReinforcingFibers 4.5 to 15  Fugitive porosity-generating component 2.5 to 8  Starch 1 to 6 Low temperature organic binder   1 to 2.5 Colloidal silica3.5 to 6.5 Water 15 to 65

The ceramic particles of the compound typically provide the ceramicpreform with wear resistance and hardness. The ceramic particles maycomprise a variety of materials, such as, for example, silicon carbide,alumina, boron carbide, or combinations or mixtures thereof. In certainembodiments, the ceramic particles comprise silicon carbide particles,360 grit.

The reinforcing fiber or whisker of the ceramic compound may includeshort or long fibers and may comprise a variety of materials, such as,for example, carbon, silicon carbide, metallic, or ceramic fibers,whiskers, or chopped filaments. The carbon fiber may be in the form ofchopped carbon tape or carbon nanotubes. In certain embodiments, thereinforcing fiber of the ceramic compound is an aluminosilicate,aluminosilica-zirconate, aluminosilica-chromate, or high purity aluminapolycrystalline fiber.

The reinforcing fiber of the ceramic compound may be prepared prior tointroducing the fiber into the batch of ceramic compound components (seeFiber Preparation step in FIG. 1). For example, when an aluminosilicaterefractory fiber is used as the reinforcing fiber, the fiber may beprepared prior to introducing the fiber into the batch. Thealuminosilicate refractory fiber is spun from an electrically meltedaluminosilicate glass. The fiber is often received from the manufacturerinterlocked together in clumps (e.g., a clumped matted bail ofrefractory fiber) and including shot glass beads left over from the meltspinning process. At least some pretreatment of the fiber may be neededbefore introducing the fiber in to the batch. For example, the fiber maybe separated and sieved to remove the shot. Further, because therefractory fiber is generally a brittle material, the fiber bundles orclumps can be broken apart by pressing on the bundle or by a sharpimpact such as from a hammermill.

In one exemplary embodiment, aluminosilicate refractory fiber washammermilled and sieved such that the clumps of the fiber were less thanabout 6 mm in length and included less shot than the bulk fiber productafter spinning. The fiber clumps were then pressed to further break downthe clumps. The pressed fiber was then screened (e.g., through a 500micron wire mesh screen) to remove loose shot (e.g., shot having adiameter greater than 500 microns). The fiber left on top of the screenwas then added to the batch of ceramic compound components. Theinclusion of this fiber in the ceramic compound resulted in a desirablemicrostructure in the MMC after infiltration of the ceramic preform witha molten metal alloy, e.g., aluminum, magnesium, titanium, copper, orany other metal discussed herein.

In certain embodiments, the reinforcing fiber or fibers may be preparedfor inclusion into the ceramic compound batch by using a wire brush orother device to gently brush off the fiber from a mat of fiber orceramic fiber paper (see Fiber Preparation step in FIG. 1). A variety offiber mats or ceramic fiber paper may be used. For example, in oneexemplary embodiment, Fiberfrax Ceramic Fiber 970J is used having athickness of about ⅛ inch, a density of about 10 lbs/ft³, a fiber indexof about 70% by weight, and an LOI including binder of 7.0. Thistechnique permits the fiber to be directly added to the compound batchas it is mixing and reduces the tendency of the fibers to agglomerate.Further, with this approach, most of the shot that is attached to thefiber has been screened out during the paper or mat making process. Thisprocess also permits the inclusion of fibers having a longer aspectratio and, depending on the fibers used, can have an advantage.

In order for the ceramic preform to be infiltrated with molten metal, itis advantageous to have high interconnected porosity which creates acontinuous pathway for the molten metal. The fugitiveporosity-generating component of the ceramic compound permits theceramic preform to have a high interconnected porosity. For example, incertain embodiments, the porosity-generating component is a carbonaceousmaterial that will burnout of the molded ceramic article during heattreatment (see, e.g., Binder Burnout and Heat Treatment steps in FIG.1). Exemplary carbonaceous materials include, but are not limited to,graphite, carbon black, graphene or organic materials with a high carboncontent such as, for example, walnut shell flour, pecan shell flour,rice hulls, and saw dust.

In certain embodiments, the low temperature organic binder of theceramic preform compound is methyl cellulose. When methyl cellulose isused, it is generally heat activated. Further, other binders that may beused include guar gum and Xanthum gum. After molding of the ceramiccompound and exposure to a temperature between about 49 and 60 degreesC. (or between about 120 and 140 degrees F.), the ceramic preformdevelops green strength which maintains its shape during handling.

The colloidal silica solution of the ceramic compound is generallyflocced with a starch, such as, for example, a cationic corn starch, toprovide a high temperature bonding system in the ceramic preform. Forexample, in certain embodiments, the colloidal silica solution includescolloidal silica particles having a negative surface charge. A cationicstarch is positively charged such that there is electrostatic attractionfor flocculation to occur. This flocced bonding system is used to bondthe refractory fibers of the ceramic compound and contributes to theformation of a cylindrical ceramic preform with a certain wallthickness. The effects of the flocculation are noticeable with a highlyloaded ceramic body and a minimum amount of water present (e.g., betweenabout 15 and 40 wt % water). As discussed in greater detail below,adding a first water amount followed by adding a second water amountwith the colloidal silica solution may contribute to the effectivenessof the flocced bonding system.

Further, the colloidal silica of the ceramic compound may also act as anadhesive. As discussed in greater detail below, the ceramic preform ofthe present application may include one or more liners or inserts atleast partially adhered to one or more surfaces of the preform. Thecolloidal silica of the ceramic compound may facilitate the adherence ofthe liner or insert to the ceramic preform. Further, greater amounts ofwater in the ceramic compound (e.g., between about 41 and 65 wt % water)may increase the adhesiveness of the ceramic compound.

The table below shows a ceramic preform compound formulation withtypical ranges given for each batch component according to an embodimentof the present application. The viscosity, batch adhesiveness, andmoldability of the compound generally changes with the level of wateraddition. For example, at a low end of water addition (e.g., betweenabout 15 and 40 wt % water), the compound is a moldable batch whichdevelops a ball-in-hand consistency. A ball-in-hand consistency isgenerally known in the art to represent an empirical determination ofthe compound's readiness for forming. A handful of material is grabbedand squeezed. If the compound knits together, it is ready to mold. Theviscosity of the low end water content material is similar to a commoncaulking compound and may range between about 5,000,000 and 10,000,000centipoise. At a high end of water addition (e.g., between about 41 and65 wt. % water), the compound has a greater fluidity with a viscositythat may range between about 250,000 and 1,500,000 centipoise. It can beappreciated that the water level content influences the consistency andease of moldability of the ceramic preform compound and the method thatis used to form a ceramic preform.

Component Weight Percentage, Wt % Silicon Carbide Particles, 360 grit 20to 55 Refractory Fiber 4.5 to 15  Burnout Material 2.5 to 8   FlakedCationic Starch 1 to 6 Methyl Cellulose   1 to 2.5 Colloidal silica 3.5to 6.5 Water 15 to 65

FIG. 2 illustrates a method 200 of preparing a ceramic preform compoundaccording to an embodiment of the present application. As shown, themethod 200 comprises the step of mixing the prepared fibers with theceramic particles. For example, in certain embodiments, silicon carbideparticles may be dry mixed with a refractory fiber, such as analuminosilicate refractory fiber, in a Hobart mixer or other suitablemixer for a period of time (e.g., less than 20 minutes).

As illustrated in FIG. 2, dry powders, such as, for example, a burnoutmaterial, starch, and binder, are added and mixed with the preparedfiber and ceramic particles. For example, in certain embodiments, thesilicon carbide particles and aluminosilicate refractory fiber are drymixed with walnut shell four, starch, and methyl cellulose in a tumblemixer or other suitable mixer for a period of time (e.g., approximately30 minutes). A US Stoneware Roller Mill, Model 755, with an enclosedcylindrical container may be used for this dry mix tumbling step. Thedry tumble mixed powders may then be added back into the Hobart mixer.

As illustrated in FIG. 2, the addition of water to the mixture isgenerally divided into two parts, a first water addition and a secondwater addition. In certain embodiments, the total amount of first wateradded to the mixture is between about 50 and about 200 grams dependingon the size of the preform ceramic compound batch. During the firstwater addition, the majority of the first water is added and the mixtureis mixed for a period of time (e.g., approximately 22 minutes). Aftermixing, the remainder of the first water is added and mixing continuesfor an additional period of time (e.g., approximately 3 minutes). Thisamount of wet mixing time (e.g., approximately 25 minutes) insures thatthe starch is completely wetted out in the batch. During the secondwater addition, a certain amount of water (e.g., between about 7 wt %and about 10 wt % of the batch composition) is mixed with the colloidalsilica solution and is added into the Hobart mixer and mixed for aperiod of time (e.g., approximately 1-2 minutes). As such, the batchclumps together and is ready to mold into a ceramic preform.

The ceramic compound may be molded using a compression molding apparatusto form a ceramic preform of the present application. FIGS. 4A-4Cillustrate a compression molding apparatus 400 according to anembodiment of the present application. As shown, the compression moldingapparatus 400 comprises a ram 402, a first or male die portion 404, anda second or female die portion 406. A ceramic compound 408 is placed inthe female die portion 406 and compressed by the male die portion 404 toform the ceramic preform 450 (see FIGS. 4C-5B). The pressure forcompression will vary depending on the consistency of the ceramiccompound 408. For example, in certain embodiments, the pressure mayrange between about 1 psi for compounds having a light consistency(e.g., higher moisture level) and about 3000 psi for compounds having aheavier consistency (e.g., lower moisture level).

As illustrated in FIGS. 4A-4C, the male die portion 404 is operativelyconnected to the ram 402 of the compression molding apparatus 400. Asshown, the apparatus 400 comprises a motor 410, e.g., a hydraulic orelectric motor, configured to selectively rotate at least a part of themale die portion 404 relative to the ram 402. For example, the motor 410may be configured to rotate the male die portion 404 about itslongitudinal axis 412 and clockwise, counterclockwise, and/or at variousspeeds relative to the ram 402. Further, the ram 402 may comprise athrust bearing or similar component that permits the male die portion404 to move and rotate when significant pressure is applied to the maledie portion. In certain embodiments, however, the male die portion 404may not be configured to rotate relative to the ram 402.

As illustrated in FIGS. 4A and 4B, the ceramic compound 408 is placed inthe bottom of the female die portion 406 and the ram 402 moves the maledie portion 404 downward. The ceramic compound 408 moves or is pushedupward in the female die portion 406 as the male die portion 404 movesdownward. As illustrated in FIG. 4B, the ceramic compound 408 fills thevoid between the male die portion 404 and the female die portion 406 asthe male die portion moves downward. In certain embodiments, the maledie portion 404 contacts the bottom of the female die portion 406 suchthat the ceramic compound 408 forms a cylindrical ceramic preform 450(see, e.g., FIGS. 4C-5B). In other embodiments, the male die portion 404stops a selected distance above the bottom of the female die portion 406such that the ceramic compound 408 forms a cylindrical ceramic preformhaving a closed end or bottom (i.e., a cup shaped ceramic preform) (see,e.g., the ceramic preform 600 shown in FIG. 6).

As illustrated in FIG. 4C, once the ceramic preform 450 is formed, themale die portion 404 retracts and an ejector 422 pushes the ceramicpreform out of the compression molding apparatus 400. As shown, theejector 422 forms at least a portion of the bottom of the female dieportion 406 and ejects the ceramic preform 450 out the top of the femaledie portion. However, the ejector 422 may be configured in a variety ofways to eject the ceramic preform 450 out the top and/or bottom of thefemale die portion 406 or compression molding apparatus 400. Further,the ceramic preform 450 may be held within the female die portion 406for a period of time (e.g., between about ½ hour and about 24 hours) oruntil it begins to dry to facilitate removal of the ceramic preform fromthe compression molding apparatus 400.

In certain embodiments, the male die portion 404 may spin or rotateabout its longitudinal axis 412 and relative to the female die portion406 as it moves downward to compress the ceramic compound 408. Further,in certain embodiments, the female die portion 406 is configured torotate or spin about its longitudinal axis 412 and relative to the maledie portion 404. As such, the compression molding apparatus 400 may beconfigured in a variety of ways to form the ceramic preform 450. Forexample, the compression molding apparatus 400 may be configured suchthat the male die portion 404 rotates relative to a stationary femaledie portion 406 during compression of the ceramic compound 408, thefemale die portion rotates relative to a stationary male die portionduring compression of the compound, and/or both the male and female dieportions rotate either in the same or opposite direction duringcompression of the compound to form the ceramic preform 450. The turningof the die portion 404 and 406 facilitates the formation of a smoothuniform surface of the ceramic preform 450. Further, the turning of thedie portion 404 and 406 permits the fibers within the ceramic compound408 to be orientated in a circular fashion to give the ceramic preform450 greater strength, e.g., hoop strength.

The compression molding apparatus 400 may comprise one or more liners orinserts on one or both of the male and female die portions 404 and 406.The liners generally adhere to one or more surfaces of the ceramicpreform, such as, for example, the inner diameter, outer diameter,and/or bottom of the ceramic preform. The liners provide support andrigidity to the ceramic preform during removal of the part from thecompression molding apparatus 400 and subsequent processing of the part.As such, the liners help the ceramic preform maintain its shape throughthe drying stage and subsequent processing steps described herein.

The liners also facilitate removal of the ceramic preform from the diemale and female portions 404 and 406. For example, during compressionwithout the liners, the ceramic compound 408 will attach or adhere tothe die portions 404 and 406. However, when the liners are positionedbetween the ceramic compound 408 and the die portions 404 and 406, thecompound will attach or adhere to the liners and not the die portions.Further, the liners may be coated with substances that facilitateremoval of the ceramic preform from the die portions 404 and 406. Forexample, low viscosity oils, mold release agents, wax, siliconlubricants or the like may be used facilitate removal of the ceramicpreform.

The liners are also configured to facilitate drying of the ceramicpreform. The liners are generally porous and absorbent to permit removalof moisture from the ceramic preform. The absorbency of the liner helpsto draw the moisture from the ceramic preform before burning theorganics out of the preform. For example, in certain embodiments, theliner permits removal of between about 25 wt % and about 75 wt % ofmoisture from the ceramic preform body. Further, the liners may becapable of being burned off the ceramic preform during subsequentprocessing of the part. In certain embodiments, the liner may be porousto permit the flow of moisture from the ceramic preform.

The liners may comprise a variety of materials, such as, for example, anon-woven material, paper, cardboard such as a cardboard tube or core,matte of aluminosilicate fiber, metal screen, or combinations thereof.Further, the liners may comprise reinforcing fibers that add strengthand rigidity to the liner and the ceramic preform. The liners may alsobe a variety of shapes and sizes, and may be configured to adhere tovirtually any surface of the ceramic preform. For example, in certainembodiments, the liners are shaped as cardboard tubes or cylinders thatadhere to the inner and outer surfaces of the ceramic preform and have athickness between about 0.003 inch and about 0.25 inch.

As illustrated in FIGS. 4A-4C, a first liner 430 shaped as a cylindricaltube is disposed about one end of the male die portion 404. As shown,the first liner 430 is received within a recessed portion 420 (see FIG.4C) of the male die portion 404 to prohibit movement of the first lineras the male die portion moves downward and compresses the ceramiccompound 408. Further, a second liner 432 shaped as a cylindrical tubeis received within the female die portion 406. As illustrated in FIGS.4C-5B, the first and second liners 430 and 432 adhere to the innerdiameter surface and the outer diameter surface, respectively, of theceramic preform 450.

In certain embodiments, a third liner may be received within the femaledie portion 406 such that the third liner at least partially adheres tothe bottom of the ceramic preform. FIG. 6 illustrates a ceramic preform600 according to an embodiment of the present application. As shown, theceramic preform 600 comprises a first liner 630 adhered to innerdiameter surface, a second liner 632 adhered to the outer diametersurface, and a third liner 634 adhered to the exterior closed end orbottom of the part. However, it should be understood that more or lessliners may be used and/or may be shaped and configured to adhere to anysurface of the ceramic preform, including the top and interior bottom ofthe part.

In certain embodiments, the ceramic preform of the present applicationmay comprise a metal core on its inner diameter and/or outer diameter toprovide additional support during the low temperature drying phase. Themetal core(s) is generally removed prior to firing the ceramic preformin the furnace.

As illustrated in FIGS. 5A and 5B, the ceramic preform 450 is formed asa hollow circular cylinder with a prescribed wall thickness T. As shown,the wall of the cylinder is substantially perpendicular to the top andbottom of the cylinder. However, in certain embodiments, the wall of thecylinder is slightly tapered (e.g., tapers from about ¼ degree to about2 degrees) to facilitate removal of the ceramic preform 450 from the dieportions. In certain embodiments, the ceramic preform 450 comprises aninner diameter ID between about 3 inches and about 8 inches; an outerdiameter OD between about 5 inches and about 20 inches; a wall height Hbetween about 3 inches and about 10 inches; and a wall thickness Tbetween about ¼ inch and about 2 inches. As described in greater detailbelow, the ceramic preform 450 may be infiltrated with a metal, such as,for example, aluminum, magnesium, titanium, or copper, and form at leasta portion of a brake drum.

The inner diameter, outer diameter, wall height, and wall thicknessdimensions of the cup shaped ceramic preform 600 illustrated in FIG. 6are generally similar to the ceramic preform 450 shown in FIGS. 5A and5B and described above. In certain embodiments, the wall of the cylinderis slightly tapered (e.g., tapers from about ¼ degree to about 2degrees) to facilitate removal of the ceramic preform 600 from the dieportions. Further, the ceramic preform 600 may also be infiltrated withmetal and form at least a portion of a brake drum. The closed end orbottom 650 of the ceramic preform 600 may or may not be removed duringsubsequent processing of the part. For example, the bottom 650 (or atleast a portion of the bottom) may provide added strength and rigidityto the ceramic preform 600 during subsequent processing of the part(e.g., during drying and heat treatment). The bottom 650, or portionthereof, may be removed to form an open ended cylinder before formingthe MMC.

FIGS. 9A and 9B illustrate a ceramic preform 900 according to anembodiment of the present application. As shown, the ceramic preform 900is shaped as a disc. In certain embodiments, the ceramic preform 900comprises an inner diameter ID between about 4 inches and about 10inches; an outer diameter OD between about 8 inches and about 14 inches;a wall height H between about ¼ inch and about 2 inches; and a wallthickness T between about 1 inch and about 5 inches. The ceramic preform900 may be infiltrated with a metal, such as, for example, aluminum,magnesium, titanium, or copper, and form at least a portion of a rotoror brake disc. For example, one or more ceramic preform 900 may be usedto form the exterior braking surface of the rotor or brake disc. Asillustrated in FIGS. 9A and 9B, liners 930 and 932 are adhered to theinner and outer surfaces, respectively, of the ceramic preform 900.

The male and female die portions 404 and 406 of the compression moldingapparatus 400 may be sized and shaped in a variety of ways to form avariety of different ceramic preforms. For example, the male and/or thefemale die portion 404 and 406 may comprise features such as raised orrecessed portions that form corresponding features in the ceramicpreform, such as, for example, a raised portion extending from the mainbody of the part or a recessed portion in the main body of the part. Incertain embodiments, the male and female die portions 404 and 406 areconfigured to form a disc shaped ceramic preform having a raisedcircular center portion. For example, FIG. 8A illustrates a side view ofa MMC brake disc 800 formed using two disc shaped ceramic preformshaving raised center portions. As shown, the raised center portions arearranged adjacent to each other to provide a channel 806 between theexterior braking surfaces of the brake disc 800 and facilitate coolingof the disc brakes.

The methods and apparatuses for forming a ceramic preform describedherein provide a dimensionally stable part. For example, the height andthickness of the ceramic preform cylindrical wall is maintainedthroughout drying, binder burnout and high temperature firing stepsdiscussed below. The ceramic preform does not slump or deform duringthese subsequent processing steps. The ratio of wall height to wallthickness of the ceramic preform is generally between about 5:1 andabout 25:1. In certain embodiments, the ratio of wall height to wallthickness of the ceramic preform is approximately 7:1. Further, theceramic preform substantially maintains its circular or round shape whenremoved from the molding apparatus and during the subsequent processingsteps. For example, the tolerance of the diameter of the ceramic preformis generally within less than 0.1 inch around the circumference of thepart. The methods and apparatuses for forming a ceramic preformdescribed herein also permit the part to have a prescribed wallthickness of 1½ inches or less when the part is released from the mold.

The methods and apparatuses for forming a ceramic preform describedherein also permit the ceramic preform to be made rapidly, such as, forexample, more than 1 preform/minute per machine, more than 2preforms/minute per machine, more than 3 preforms/minute per machine, orat least 3 preforms/minute per machine. As such, these methods andapparatuses provide for the rapid production of ceramic preforms athigher volumes than conventional processes. Further, the ceramicpreforms produced by the methods and apparatuses described herein have agreater stiffness than ceramic preforms made by conventional processes.

FIG. 3A illustrates an exemplary method 300 of forming a ceramic preformthat includes placing one or more liners on the male die portion and/orin the female die portion of the compression molding apparatus. Aceramic compound is placed in the female die portion of the compressionmolding apparatus. The ceramic compound is compressed with the male dieportion to form a ceramic preform of the present application. Theceramic preform is removed from the female die portion with the one ormore liners attached to the ceramic preform. In certain embodiments, themale die portion and/or the female die portion of the compressionmolding apparatus is rotated during compression of the ceramic compound.

FIG. 3B illustrates an exemplary method 350 of forming a ceramic preformthat includes placing a ceramic preform in the female die portion of thecompression molding apparatus. The male die portion and/or the femaledie portion of the compression molding apparatus is rotated and theceramic compound is compressed with the male die portion to form aceramic preform of the present application. The ceramic preform isremoved from the female die portion. In certain embodiments, one or moreliners are placed on the male die portion and/or in the female dieportion of the compression molding apparatus and the ceramic preform isremoved from the female die portion with the one or more liners attachedto the ceramic preform.

Another exemplary method of forming a ceramic preform includes using acompression molding apparatus to compress the ceramic compound withoutrotating the male or female die portions of the apparatus. For example,in certain embodiments, male and female mold halves are closed on apress. The sidewalls of the female mold have approximately a 2 degreetaper to facilitate removal of the ceramic preform from the mold afterforming. The ceramic compound is introduced into the female mold andinserts or liners may or may not be used on the circumference of thefemale mold, the bottom surface of the female mold, and/or the outersurface of the male mold. The male mold is placed on top of the ceramiccompound in the female mold. The mold assembly is placed in a press.Pressure is slowly applied such that the ceramic compound begins to moveup the sidewalls to the male mold top plate until the batch flash comesout of the parting line between the male top plate and the female mold.The male and female mold halves are substantially closed. After thebatch flash stops moving, the pressure is maintained for a period oftime (e.g., approximately 30 seconds) and the mold assembly is releasedfrom the press. The male mold is removed leaving the ceramic preform inthe female mold. The ceramic preform is dried in the female mold. Theceramic preform is released from the female mold. In certainembodiments, the ceramic preform is cup-shaped with tapered side walls.The cup-shaped ceramic preform goes through the further process steps ofbinder burnout and high temperature firing described below. Further, thebottom of the ceramic preform may or may not be removed to form anopen-ended cylinder.

As illustrated in FIG. 1, after the ceramic preform is released from thecompression molding apparatus, the ceramic preform goes through thefurther process steps of drying, binder burnout, and heat treatment. Theceramic preform is generally dried in the drying oven at a certaintemperature (e.g., about 60 degrees C. or about 140 degrees F.) for aperiod of time. The length of the oven drying time will often vary basedon the water content of the ceramic preform, the size of the part and,if one or more liners are used, the rate at which the water permeatesthrough the liners. A ceramic preform is generally considered dry whenthe weight loss is between about 20 and about 70 wt % due to the removalof water from the part.

During the binder burnout step illustrated in FIG. 1, a low temperatureheat treatment is conducted to remove the organics or volatilecomponents from the ceramic preform. In certain embodiments, theseorganics include the walnut shell flour, the starch, and the methylcellulose. The low temperature heat treatment cycle is generally anapproximately 1 hour ramp to a certain temperature (e.g., about 260degrees C. or about 500 degrees F.) with an approximately two hour holdat about the same temperature. A high temperature heat treatment isconducted to seal the ceramic bond created by the colloidal silica. Thehigh temperature heat treatment generally has a hold at a certaintemperature (e.g., about 985 degrees C. or about 1800 degrees F.) forapproximately two hours. In certain embodiments, after the hightemperature heat treatment, the colloidal silica particles remain in theceramic preform and the ceramic preform comprises silicon carbideparticles, refractory fiber and silica bond. In these embodiments, theburnout materials, starch, methyl cellulose, and (if used) the linersare all removed from the porous ceramic preform body after the low andhigh temperature heat treatments.

The ceramic preform of the present application may be infiltrated with ametal, such as, for example, aluminum, magnesium, titanium, or copper,to form a MMC of the present application. For example, the ceramicpreform may be introduced into a die-casting mold for infiltration ofmetals that are capable of being die cast, such as, for example,aluminum, magnesium, or copper, to form a MMC of the presentapplication.

A high pressure die cast mold generally includes two die parts: a firstdie part that is generally stationary and coupled to a non-moving platenof the die casting machine and a second die part that is movablerelative to the first die part and is generally coupled to a movableplaten of the die casting machine. Within each die part is a mold cavitythat receives the injected molten metal. The mold cavity isrepresentative of the final product shape with calculated shrinkfactored in and draft added to aid in part release. In certainembodiments, the amount of shrinkage is between about 0.07% and about2.19%. The cavity also generally includes a nesting area that acceptsand locates the ceramic preform within the mold cavity.

The first die part or stationary part generally includes a pathway formolten metal to travel to fill the mold, a piston type shot tip thatmoves the molten metal into the mold, and an ejection system that aidsejecting the finished casting after solidification. Further, the seconddie part of moving part generally has a vacuum system to facilitateevacuation of air trapped within the mold cavity after the ceramicpreform is placed therein and the mold is closed before the molten metalis injected.

The die parts are typically machined from tool steel with varioustreatments to improve durability. Heating and cooling circuits may alsobe added throughout the die parts to aid in attaining and retainingoptimum temperatures for the casting process. These circuits may usevarious fluids to transfer temperatures into or out of predeterminedareas of the die and are typically placed close to the mold cavity butdo not enter the cavity.

The ceramic preform is placed within the mold cavity of the die castmold. The ceramic preform may be preheated to a certain temperatureprior to introduction into the mold cavity. For example, the ceramicpreform may be preheated to a temperature that is above the temperatureof the molten metal that is being injected into the mold cavity (e.g.,aluminum). In certain embodiments, the ceramic preform is heated to atleast 50 degrees F. above the temperature of the molten metal that isbeing injected into the mold cavity. In other embodiments, the ceramicpreform is heated to at least 100 degrees F. above the temperature ofthe molten metal that is being injected into the mold cavity. Moltenmetal is then injected into the mold cavity at a low velocity andinfiltrates the porous body of the ceramic preform. The velocity of themolten metal is such that the ceramic preform does not deform duringinjection of the molten metal. The molten metal infiltratessubstantially through the entire wall thickness. Further, in certainembodiments, the molten metal infiltrates substantially through aceramic preform having a wall thickness of 1% inches or less.

FIG. 7 illustrates a side cross sectional view of a MMC brake drum 700according to an embodiment of the present application. As shown, acylindrical ceramic preform 702 of the present application forms atleast a portion of the braking surface of the brake drum 700. Theceramic preform 702 was infiltrated with a metal (e.g., aluminum) toform the MMC brake drum 700, such as during a die casting process asdiscussed herein.

The ceramic preform 702 and MMC brake drum 700 may be a variety of sizesand shapes for a variety of different vehicles. For example, in certainembodiments, the MMC brake drum 700 may be configured for use with alarge truck or military vehicle, e.g., with vehicles having brake drumsabout 16% inches in diameter D₁ and either about 5 inches or about 7inches deep D₂. In these embodiments, the inner diameter of thecylindrical ceramic preform 702 may be between about 12 inches and about17 inches and the preform may weigh between about 10 lbs. and about 15lbs. Further, the wall thickness of the cylindrical ceramic preform 702may be between about ½ inch and about 1½ inches or more and the wallheight may be between about 4 inches and about 8 inches. In certainembodiments, the ratio of the height of the cylindrical wall and thewall thickness of the ceramic preform 702 for a brake drum is betweenabout 5:1 to about 12:1, or about 7:1 in one exemplary embodiment. Incertain embodiments, the MMC brake drum 700 is greater than about 10inches in diameter and greater than about 1 inch deep.

FIGS. 8A and 8B illustrate a MMC brake disc 800 according to anembodiment of the present application. The brake disc comprises two MMCdiscs 802 having raised center portions 804. As shown, the centerportions 804 are arranged adjacent to each other to provide a channel806 between the exterior braking surfaces of the brake disc. The channel806 facilitates cooling of the disc brakes. Further, as illustrated inFIG. 8B, each MMC disc 802 may comprise raised portions 808 that theform vanes to facilitate airflow and cooling of the disc brakes as thebrake disc 800 rotates.

As discussed above, each MMC disc 802 is formed using a disc shapedceramic preform having approximately the same shape as the MMC disc.Each ceramic preform was infiltrated with a metal (e.g., aluminum) toform the MMC disc 802, such as during a die casting process as discussedherein. The ceramic preform and MMC brake disc 800 may be a variety ofsizes and shapes for a variety of different vehicles. For example, incertain embodiments, the MMC brake disc 800 is between about 9 inchesand about 16 inches in diameter and between about 1 inch and about 1½inches thick.

As an example, a cylindrically cup-shaped ceramic preform with a bottomwas made using a two-part mold having a female receptacle that formedthe outside surface of the part and a male insert that defined the innerwall surface of the ceramic part. A preform ceramic compound wasintroduced into the mold. The ceramic compound was a high viscosity, lowwater content ceramic preform compound formulation and was made bycombining 47.63 wt % Silicon Carbide 360 grit particles (WashingtonMills Carborex 360), 9.53 wt % hammermilled and sieved aluminosilicaterefractory fiber (Morgan Thermal Ceramics Cerafiber HM6), −5.4 wt %walnut shell flour −100 mesh (Echo-Shell, Inc.), 3.63 wt % flakedcationic corn starch (Wesbond Westar+3), 1.77 wt % hydroxypropyl methylcellulose (Dow Chemical Methocel™ A4M), 11.3 wt. % of first wateraddition, 9.64 wt % of second water addition and 11.1 wt. % colloidalsilica solution (Wesbond Bindzil® 1440). The mold was pressed in aconventional press to a static pressure sufficient to move the ceramiccompound up the sidewalls of the mold to form the sidewalls of the part.The sidewalls of the mold were tapered approximately 2° to permit easyrelease of the part from the mold. The mold from which the ceramic partwas made was approximately 4 inches tall with an outer diameter at thetop of about 5¼ inches and an outer diameter at the base of about 5inches. The wall thickness of the mold was about 0.4 inch. The bottomwall thickness of the mold was about ¼ inch. The weight of the ceramicpart after all processing steps, including drying, low temperaturefiring and high temperature firing, was about 520 grams, or 518.4 grams.The composition of the final part was 77.3 wt % Silicon Carbide, 15.5wt. % aluminosilicate refractory fiber, and 7.2 wt % silicate binder.

As an example, a cylindrically cup-shaped ceramic preform with a bottomwas made using a compression molding apparatus. A preform ceramiccompound was made and introduced into the mold. The ceramic compound wasa low viscosity, high water content ceramic preform compound formulationand was made by combining 35.25 wt % Silicon Carbide 360 grit particles(Washington Mills Carborex 360), 7.07 wt % hammermilled and sievedaluminosilicate refractory fiber (Morgan Thermal Ceramics CerafiberHM6), 3.99 wt % walnut shell flour −100 mesh (Echo-Shell, Inc.), 2.19 wt% flaked cationic corn starch (Wesbond Westar+3), 1.41 wt %hydroxypropyl methyl cellulose (Dow Chemical Methocel™ A4M), 35.25 wt. %of first water addition, 9.26 wt % of second water addition and 11.1 wt.% colloidal silica solution (Wesbond Bindzil® 1440). The male topportion of the die was rotated while applying a gentle downward force.The preform ceramic compound was pushed upwards to form the sidewalls ofthe cylinder. The ceramic part was dried, fired for binder burnout, andfired at high temperature. The resulting finished part had a weight ofapproximately 280 grams, or 280.8 grams. The height of the ceramicpreform sidewall and the sidewall thickness were 98.53 mm and 8.95 mmrespectively for a height to thickness ratio of about 11:1. Thecomposition of the final part was 79.1 wt % SiC, 15.9 wt. %aluminosilicate refractory fiber and 5.0 wt % silicate binder.

As an example, a cylindrically cup-shaped ceramic preform with a bottomwas made using a compression molding apparatus. The mold was lined onthe outside wall surface and the bottom with cardboard. After drying,the ceramic part released easily from the metal mold with the cardboardadhering to the ceramic part. After drying of the cardboard encasedceramic part, the part weight was 250.5 grams. The height of the ceramicpreform wall was 97.73 mm and the wall thickness was 9.63 mm for a wallheight to thickness ratio of about 10:1.

As an example, a ceramic preform nominally measuring 4 in.×4 in.×1 in.was infiltrated with molten aluminum to make an aluminum MMC. Theceramic preform was made with preform ceramic compound of the presentapplication. The surface of the preform was sanded on one large areaside. The ceramic preform which had been preheated to an elevatedtemperature was introduced into a die-casting mold. Aluminum alloy 380was infiltrated into the ceramic preform by squeeze-casting. The metalinfiltration through the highly porous ceramic preform occurred throughthe thickness of the preform to a depth of 0.962 to 0.978 inches.

In certain embodiments, a method of making a ceramic preform used in themanufacture of a metal matrix composite brake drum, disc brake rotor, orcomponent thereof comprises utilizing a compression molding apparatushaving a male die portion and a female die portion. At least one of themale die portion and the female die portion are configured to rotaterelative to the other die portion and about its longitudinal axis. Atleast a portion of an inner surface of the female die portion is linedwith a first porous and absorbent liner such that at least a portion ofthe first liner attaches to an outer diameter of the ceramic preform andfacilitates removal of the ceramic preform from the female die portion.At least a portion of an outer surface of the male die portion is linedwith a second porous and absorbent liner such that at least a portion ofthe second liner attaches to an inner diameter of the ceramic preformand facilitates removal of the ceramic preform from the male dieportion. A ceramic compound is placed in the female die portion. Theceramic compound comprises between about 20 Wt % and about 55 Wt %ceramic particles; between about 4.5 Wt % and about 15 Wt % reinforcingfibers; between about 2.5 Wt % and about 8 Wt % fugitive porositygenerating component; between about 1 Wt % and about 6 Wt % starch;between about 1 Wt % and about 2.5 Wt % low temperature organic binder;between about 3.5 Wt % and about 6.5 Wt % colloidal silica; and betweenabout 15 Wt % and about 65 Wt % water. The ceramic compound iscompressed with the male die portion to form the ceramic preform. Atleast one of the male die portion and the female die portion rotatesrelative to the other die portion and about its longitudinal axis duringcompression of the ceramic compound. The ratio of wall height to wallthickness of the ceramic preform is between about 5:1 and about 25:1.The ceramic preform is removed from the compression molding apparatus.The first liner is attached to the outer diameter of the ceramic preformand the second liner is attached to the inner diameter of the ceramicpreform. The ceramic preform is dried in an oven until the weight losspercentage due to the removal of the water from the ceramic preform isbetween about 20 percent and about 70 percent. The ceramic preform isheat treated at a temperature sufficient to remove the fugitive porositygenerating component, starch, and low temperature organic binder fromthe ceramic preform. The ceramic preform is heat treated at atemperature sufficient to seal the ceramic bond created by the colloidalsilica. The first liner and the second liner are removed from theceramic preform during heat treatment. The method may also comprisemixing the components of the ceramic compound, brushing the reinforcingfibers off a ceramic fiber paper, and adding the brushed reinforcingfibers to the ceramic compound.

In certain embodiments, a method of making a metal matrix compositebrake drum, disc brake rotor, or component thereof comprises the stepsdescribed above for making a ceramic preform. Further, the ceramicpreform is preheated to a certain temperature and then placed in a moldcavity of a high pressure die cast mold. Molten metal is injected intothe mold cavity such that the metal infiltrates substantially throughthe entire wall thickness of the ceramic preform.

As described herein, when one or more components are described as beingconnected, joined, affixed, coupled, attached, or otherwiseinterconnected, such interconnection may be direct as between thecomponents or may be in direct such as through the use of one or moreintermediary components. Also as described herein, reference to a“member,” “component,” or “portion” shall not be limited to a singlestructural member, component, or element but can include an assembly ofcomponents, members or elements.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the invention to such details.Additional advantages and modifications will readily appear to thoseskilled in the art. For example, where components are releasably orremovably connected or attached together, any type of releasableconnection may be suitable including for example, locking connections,fastened connections, tongue and groove connections, etc. Still further,component geometries, shapes, and dimensions can be modified withoutchanging the overall role or function of the components. Therefore, theinventive concept, in its broader aspects, is not limited to thespecific details, the representative apparatus, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of theapplicant's general inventive concept.

While various inventive aspects, concepts and features of the inventionsmay be described and illustrated herein as embodied in combination inthe exemplary embodiments, these various aspects, concepts and featuresmay be used in many alternative embodiments, either individually or invarious combinations and sub-combinations thereof. Unless expresslyexcluded herein all such combinations and sub-combinations are intendedto be within the scope of the present inventions. Still further, whilevarious alternative embodiments as to the various aspects, concepts andfeatures of the inventions—such as alternative materials, structures,configurations, methods, devices and components, alternatives as toform, fit and function, and so on—may be described herein, suchdescriptions are not intended to be a complete or exhaustive list ofavailable alternative embodiments, whether presently known or laterdeveloped. Those skilled in the art may readily adopt one or more of theinventive aspects, concepts or features into additional embodiments anduses within the scope of the present inventions even if such embodimentsare not expressly disclosed herein. Additionally, even though somefeatures, concepts or aspects of the inventions may be described hereinas being a preferred arrangement or method, such description is notintended to suggest that such feature is required or necessary unlessexpressly so stated. Still further, exemplary or representative valuesand ranges may be included to assist in understanding the presentdisclosure, however, such values and ranges are not to be construed in alimiting sense and are intended to be critical values or ranges only ifso expressly stated. Moreover, while various aspects, features andconcepts may be expressly identified herein as being inventive orforming part of an invention, such identification is not intended to beexclusive, but rather there may be inventive aspects, concepts andfeatures that are fully described herein without being expresslyidentified as such or as part of a specific invention, the inventionsinstead being set forth in the appended claims. Descriptions ofexemplary methods or processes are not limited to inclusion of all stepsas being required in all cases, nor is the order that the steps arepresented to be construed as required or necessary unless expressly sostated. The words used in the claims have their full ordinary meaningsand are not limited in any way by the description of the embodiments inthe specification.

1. A method of making a ceramic preform for a vehicle component, themethod comprising: utilizing a compression molding apparatus having afirst die portion having a first molding surface and a second dieportion having a second molding surface; placing one or more porousliners between a ceramic compound and at least one of the first moldingsurface and second molding surface; compressing the ceramic compoundbetween the first and second die portions to form a ceramic preformhaving the one or more liners disposed on an external surface of theceramic preform; removing the ceramic preform from the compressionmolding apparatus, wherein the one or more porous liners are attached tothe external surface of the ceramic preform; and wherein the ceramiccompound comprises ceramic particles, reinforcing fibers, organicmaterials, and water; and wherein the one or more porous liners areabsorbent and draw moisture away from the external surface of theceramic preform, maintain the shape of the ceramic preform, and arecapable of being burned off of the ceramic preform during heat treatmentof the ceramic preform.
 2. The method of claim 1, wherein the ceramicpreform is compressed between two porous liners.
 3. The method of claim1, wherein the one or more porous liners are non-ceramic.
 4. The methodof claim 1, wherein the one or more porous liners are formed ofcardboard.
 5. The method of claim 1, wherein the first die portioncomprises a male die portion and the second die portion comprises afemale die portion.
 6. The method of claim 1, wherein the ceramiccompound is formed as either a cylinder or a tube.
 7. The method ofclaim 6, wherein the one or more porous liners are formed as either acylinder or a tube.
 8. The method of claim 1, further comprising thestep of: infiltrating the ceramic preform with molten metal to form thevehicle component, wherein the infiltrated preform forms a metal matrixcomposite portion of the vehicle component.
 9. The method of claim 8,wherein the metal matrix composite portion comprises at least a portionof an external surface of the vehicle component.
 10. The method of claim8, wherein the molten metal is an aluminum alloy.
 11. The method ofclaim 8, wherein the vehicle component is a rotating vehicle component.12. The method of claim 11, wherein the rotating vehicle component is abrake component.
 13. The method of claim 12, wherein the metal matrixcomposite portion comprises at least a portion of a braking surface ofthe brake component.